1. Field of the Invention
The present invention relates to an optical recording medium excellent in a humidity resistance and a method of manufacturing the same, and in particular, to an optical recording medium having a recording film including an organic dye and a method of manufacturing the same.
2. Description of the Related Art
An organic dye such as a cyanine dye or a phthalocyanine dye is used as composition of a recording film of a so-called WORM (Write Once Read Multiple) type optical recording medium.
Writing in the WORM type optical recording medium is performed by irradiating and collecting a laser beam onto a fine section of the recording film, and then transforming the laser beam into thermal energy to change the recording film in its condition (i.e. forming pits on the surface of the recording film). In order to smoothly change the recording film in its condition, two sets of substrates, on each of which a recording film is formed, are prepared and arranged in such a manner that the recording films thereof face each other, like a so-called air sandwitching structure.
The laser beam used for writing in the above-mentioned WORM type optical recording medium is irradiated in the direction from the side of the substrate so as to form pits optically readable in the recording film. The output of the laser beam used for reading to reproduce the recorded data is weaker than that used for writing, and the contrast between the portion provided with the pit and the portion without the pit can be read as an electric signal.
In addition, there is another type of a so-called ROM (Read Only Memory) type optical recording medium in which data was recorded in advance, which is different from the above-mentioned WORM type optical recording medium and which is used in the fields of the voice recording and the information processing. The above-mentioned ROM type medium does not have a writable recording film. More specifically, in the ROM type medium, pre-pits which correspond to the data to be reproduced are formed on the substrate made of plastics by an injection molding, then a reflecting film made of metal such as Au, Ag, Cu, Al and the like are formed thereon, and then a protection film is further formed thereon. The Compact Disk which is a so-called CD is the typical medium of the ROM type medium. The specification of the signal for recording and reading the CD is standardized, and the reproducing apparatus of the CD based on this standard is used as a Compact Disk player (CD player).
The above-mentioned WORM type optical recording medium as well as the CD uses a laser beam. A configuration of the WORM type optical recording medium as well as the CD is a disk type. Accordingly, there may be developed a WORM type optical recording medium which satisfies the standard of the CD specification and can be used in the CD player without any additional equipment.
More specifically, various studies are made on the WORM type optical recording medium including a light transmissive substrate, a recording film including an organic dye formed on the substrate, a reflective film formed on the recording film and a protecting film formed on the reflective film.
As a solvent for dye material forming the recording film of the WORM type optical recording medium, for example, diacetone alcohol, 2-ethoxyethanol, 2-methoxyethanol, isophorone, methanol, 2,2,3,3-tetrafluoro-1-propanol and the like are appropriately selected and used.
Since the signals of the above-mentioned optical recording medium is reproduced in the CD player mounted on the vehicle, it is required to be excellent in a environmental resistance.
However, the above-mentioned WORM type optical recording medium is rather poor in this environmental resistance.